Recent advances in theory and experimen- tation motivate a thorough reassessment of the physics of debris flows. Analyses of flows of dry, granular solids and solid-fluid mixtures provide a foundation for a com- prehensive debris flow theory, and experiments provide data that reveal the strengths and limitations of theoret- ical models. Both debris flow materials and dry granular materials can sustain shear stresses while remaining stat- ic; both can deform in a slow, tranquil mode character- ized by enduring, frictional grain contacts; and both can flow in a more rapid, agitated mode characterized by brief, inelastic grain collisions. In debris flows, however, pore fluid that is highly viscous and nearly incompress- ible, composed of water with suspended silt and clay, can strongly mediate intergranular friction and collisions. Grain friction, grain collisions, and viscous fluid flow may transfer significant momentum simultaneously. Both the vibrational kinetic energy of solid grains (mea- sured by a quantity termed the granular temperature) and the pressure of the intervening pore fluid facilitate motion of grains past one another, thereby enhancing debris flow mobility. Granular temperature arises from conversion of flow translational energy to grain vibra- tional energy, a process that depends on shear rates, grain properties, boundary conditions, and the ambient fluid viscosity and pressure. Pore fluid pressures that exceed static equilibrium pressures result from local or global debris contraction. Like larger, natural debris flows, experimental debris flows of ;10 m 3 of poorly sorted, water-saturated sediment invariably move as an unsteady surge or series of surges. Measurements at the base of experimental flows show that coarse-grained surge fronts have little or no pore fluid pressure. In contrast, finer-grained, thoroughly saturated debris be- hind surge fronts is nearly liquefied by high pore pres- sure, which persists owing to the great compressibility and moderate permeability of the debris. Realistic mod- els of debris flows therefore require equations that sim- ulate inertial motion of surges in which high-resistance fronts dominated by solid forces impede the motion of low-resistance tails more strongly influenced by fluid forces. Furthermore, because debris flows characteristi- cally originate as nearly rigid sediment masses, trans- form at least partly to liquefied flows, and then trans- form again to nearly rigid deposits, acceptable models must simulate an evolution of material behavior without invoking preternatural changes in material properties. A simple model that satisfies most of these criteria uses depth-averaged equations of motion patterned after those of the Savage-Hutter theory for gravity-driven flow of dry granular masses but generalized to include the effects of viscous pore fluid with varying pressure. These equations can describe a spectrum of debris flow behav- iors intermediate between those of wet rock avalanches and sediment-laden water floods. With appropriate pore pressure distributions the equations yield numerical so- lutions that successfully predict unsteady, nonuniform motion of experimental debris flows.

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The physics of debris flows

Particle reinforced metal matrix composites are now being produced commerically, and in this paper the current status of these materials is reviewed. The different types of reinforcement being used, together with the alternative processing methods, are discussed. Depending on the initial processing method, different factors have to be taken into consideration to produce a high quality billet. With powder metallurgy processing, the composition of the matrix and the type of reinforcement are independent of one another. However, in molten metal processing they are intimately linked in terms of the different reactivities which occur between reinforcement and matrix in the molten state. The factors controlling the distribution of reinforcement are also dependent on the initial processing method. Secondary fabrication methods, such as extrusion and rolling, are essential in processing composites produced by powder metallurgy, since they are required to consolidate the composite fully. Other methods, suc...

Particle reinforced aluminium and magnesium matrix composites

Responding to the latest developments in rock physics research, this popular reference book has been thoroughly updated while retaining its comprehensive coverage of the fundamental theory, concepts, and laboratory results. It brings together the vast literature from the field to address the relationships between geophysical observations and the underlying physical properties of Earth materials - including water, hydrocarbons, gases, minerals, rocks, ice, magma and methane hydrates. This third edition includes expanded coverage of topics such as effective medium models, viscoelasticity, attenuation, anisotropy, electrical-elastic cross relations, and highlights applications in unconventional reservoirs. Appendices have been enhanced with new materials and properties, while worked examples (supplemented by online datasets and MATLAB® codes) enable readers to implement the workflows and models in practice. This significantly revised edition will continue to be the go-to reference for students and researchers interested in rock physics, near-surface geophysics, seismology, and professionals in the oil and gas industries.

The Rock Physics Handbook

Transport characteristics of suspension: VIII. A note on the viscosity of Newtonian suspensions of uniform spherical particles

One-dimensional drift-flux model and constitutive equations for relative motion between phases in various two-phase flow regimes

Heat-transfer and pressure-drop measurements were made with non- Newtonian aqueous theorium oxide suspensions. A comparison of the results of the two different kinds of measurement allowed thee general features of nonNewtonian thorium oxide suspension heat transfer to be readily identified, thus leading to a clear understanding of anomalies observed in jkprevious suspension heat- transfer studies. Data were obtained at suspension concentrations up to 0.10 volume fraction solids, (1,000 g. of thorium/kg. of water) in systems having tube diameters of 0.318 and 1.030 in. In addition laminar-flow data were taken with a capillary-tube viscometer with a tube diameter of 1/8 in. and an L/D of 1,000. It was shown that laminar flow physical properties determined with the 1/ 8 in. diameter tube were satisfactory for correlating data taken with tubes up to 1.030 in. in diameter. Until the present study, information was not available which would permit a choice between two different viscosities for use in correlating nonNewtonian turbulent heat transfer and flow data. The limiting viscosity at very high shear rates is shown to give a unique correlation of turbulent data for tube diameters from 0.124 to 1.030 in., whereas the use of the effective viscosity at very high shearmore » rates is shown to value of the wall shear stress corresponding to each given flow condition) gives a pronounced diameter effect in turbulent-flow correlations. The data show that the onset of turbulence for both the pressure-drop and heat-transfer measurements occurs at the same Reynolds number and is approximated by the value predicted by the Hedstrom criterion (II). The heat-transfer transition region extends to Reynolds numbers a factor of four times greater than the critical, as is also the case with Newtonian materials. Heat transfer to thorium oxide slurries in fully developed turbulent flow is the same as that predicted by the usual correlations for Newtonian fludds to within the precision of the experimental data, provided that the Reynolds and Prandtl numbers are calculated with the limiting viscosity at high rates of shear, , for this viscosity. An approximate form of Martinelli's momentum heat transfer analogy correlates the experimental results within +17 and -36%. (auth)« less

Heat and momentum transport characteristics of non‐Newtonian aqueous thorium oxide suspensions

The minimum transport velocity was determined for flocculated thorium oxide and kaolin suspensions flowing in glass pipes. The pipes ranged from 1 to 4 in. in diameter, and the concentration was varied from 0.01 to 0.17 volume fraction solids. Two flow regimes were observed depending on the concentration of the suspension. In the first the suspension was sufficiently concentrated to be in the compaction zone and hence had an extremely low settling rate. The second regime was observed with more dilute suspensions which were in the hindered-settling zone and settled ten to one-hundred times faster than slurries which were in compaction. The concentration for transition from one regime to the other was dependent on both the tube diameter and the degree of flocculation. The suspension particles were smaller than the thickness of the laminar sublayer, and they settled according to Stokes' law for the particular conditions of this study. Under these circumstances the relation developed for dilute suspensions is consistent with particle transfer in the radial direction owing to Bernoulli forces on the particle and the action of turbulent fluctuations which penetrate the laminar sublayer. For concentrated suspension in compaction the minimum transport velocity was given by a characteristic criticalmore » Reynolds number. (auth)« less

Transport characteristics of suspensions: ii. minimum transport velocity for flocculated suspensions in horizontal pipes

Both the rheological and the hindered-settling characteristics of small particle size suspensions (0.1 to 50 μ) are primarily determined by the degree of flocculation and the concentration of the suspension. Previous studies have shown that when the laminar shear diagrams are fitted by the Bingham plastic model, the parameters τy/ϕ3 and ϕ−1 In η/μ are constants which are proportional to the degree of flocculation

The present study showed that these rheological parameters were proportional to the value of α determined from the hindered-settling measurements (α is defined as the ratio of the volume of fluid immobilized by the floc structure to the volume of solids in the floc structure). The materials studied included suspensions of thorium oxide in water and methanol and of titania, kaolin, alumina, and graphite in water. The particle size range was from 0.40 to 17.0 μ

Values of the attractive force between particles calculated from the rheological and hindered-settling data were in good agreement with each other and with the theoretical values calculated from the Derjaguin-Verwey-Overbeek theory of colloid stability. The good agreement among the different values suggests that the present approach may be generally applicable to a variety of different systems.

Transport characteristics of suspensions VII. Relation of hindered‐settling floc characteristics to rheological parameters

The local and the average rates of forced convection through laminar boundary layers on a flat plate were shown to be markedly increased by locating small cylinders near the outer edge of the boundary layer. The local rate of forced convection was strongly peaked directly beneath each cylinder; the magnitude of the effect depended upon the free stream velocity, the spacing between cylinders, and the gap between the cylinders and the plate. Under optimum conditions, local values of the rate of forced convection were increased as much as 340%, while the average values were increased by over 190%.

Forced convection mass transfer: Part II. Effect of wires located near the edge of the laminar boundary layer on the rate of forced convection from a flat plate

David G. Thomas

Papers

Transport characteristics of suspension: VIII. A note on the viscosity of Newtonian suspensions of uniform spherical particles

Heat and momentum transport characteristics of non‐Newtonian aqueous thorium oxide suspensions

Transport characteristics of suspensions: ii. minimum transport velocity for flocculated suspensions in horizontal pipes

Transport characteristics of suspensions VII. Relation of hindered‐settling floc characteristics to rheological parameters

Forced convection mass transfer: Part II. Effect of wires located near the edge of the laminar boundary layer on the rate of forced convection from a flat plate